The present invention relates to an artificial light source which incorporates a transmissive holographic optical element to provide improved control over the pattern of radiation from the source. Related inventions are described in my prior U.S. Pat. No. 4,536,833 and in my copending application Ser. Nos. 897,294, 897,296 and 897,292.
As used in this application, an artificial light source comprises an emissive material as a source of radiation, and an envelope surrounding the emissive material. Known artificial light sources within this definition include incandescent, fluorescent and high intensity discharge lamps. The term artificial light source as used in this application does not include fixtures which support the light source and facilitate the supply of power to the light source.
Current state of the art lighting and lamp design relies principally on the use of fixtures containing conventional reflectors and lenses to control the distribution of radiation. These fixtures, however, reduce the lighting efficiency of the light source since much of the radiation is reflected back into the fixture and lost as heat. Furthermore, heat build-up within the fixture can lead to a decrease in the life of the light source.
Some incandescent lamps, such as certain spot lights, may have a reflector and a conventional lens incorporated as integral parts of the light source. These lamps are still subject to substantial efficiency loss and heating, however, because of the nature of the conventional optical elements used. For example, the effect of a conventional lens on radiation depends entirely on the angle of incidence of the radiation. Radiation striking the lens over a certain range of angles will be diffracted roughly toward the task area. Outside of this range, however, radiation is either directed to a point outside the task area, or is reflected back into the lamp. The first of these effects leads to efficiency loss, the second to efficiency loss and heating.